The advent of heavy-duty, high volume earth moving and grading equipment has greatly increased the efficiency of earth grading operations involved in the construction of highways and in the preparation of tracts of land for building or farming, or for other uses. The introduction of the laser into grading operations dramatically simplified the grading of flat parcels of land and significantly increased the accuracy with which the grading can be accomplished. Not withstanding these great advances, however, the actual work of grading land still requires a great deal of manual labor and site surveying and pre-preparation.
The approach to preparing a tract for grading and for grading the tract has, with a few significant exceptions, remained unchanged for several decades. Generally speaking, the following steps are used in most grading operations. Once the tract perimeter has been defined by traditional surveying method, and a determination as to the ultimately desired utilization of the tract has been made, an engineering study is undertaken to determine the feasibility of preparing the tract for the desired utilization and to define the ultimate, graded configuration of the tract. (It should be noted that in the present discussion, reference will be made to a tract of land and the invention described hereinafter will be described with reference to the preparation of a tract of land for residential use. It will be understood, however, that the term "tract" is of general application, and would refer to any tract or area of land which requires site preparation. This would include the construction of freeways, building pads, fields for agricultural use, runways for airport use, construction of dams or other conservation projects, etc.)
The engineering phase of site preparation results in plans and specifications which define the configuration of the site in its desired final form. The plans and specifications would, typically, comprise one or more tract plans which are, in effect, a view of the site from directly overhead, i.e., a plan view, and one or more elevational views, if significant elevational structure is involved, taken along vertical planes which intersect the planned view at various desired locations. These plans define the ultimate, or, as used herein, the "target" configuration of the site by means of a number of individual points, each of which is defined by northing and easting coordinates, including the elevational and slope defining data. These coordinates define each location on the tract in terms which correspond, conceptually with the lateral and longitudinal location of the point. By a separate set of specifications an elevational index assigns to each coordinate an elevation and the cross slope of the grade at that point. It is common practice now, to define the tract in terms of "northing" and "easting" points, each of which northing and easting points may be assigned a corresponding spot elevation. Elevations are typically identified by spot elevations, contour lines and/or grade break lines. The northing and easting of a given point is defined as the distance north and the distance east from a reference point which may be located in the southwest corner of the tract being graded. The elevational point may be defined in absolute terms, i.e., distance above sea level, or in relative terms giving an elevation above or below a given reference point. The same reference point may be used from which all northing and easting points and all elevational points are measured. Drawings may also be prepared which show in perspective or isometrically the ultimate configuration of the tract. Modern electronic data processing techniques and sophisticated programs can generate perspective and isometric views of a tract from the northing, easting and elevational data provided in the engineering study. The engineering study also provides a great deal of additional information which is not particularly germane to the present invention. For example, the engineering study will result in information as to the amount of earth which must be moved, the amount of fill which must be accomplished, whether or not earth will need to be moved onto the tract to accomplish sufficient filling or removed from the tract, etc. These data are, of course, very important in obtaining competitive bids and in projecting the costs of a given project.
Thus, from the engineering study, one skilled in reading engineering drawings and tract specifications, can determine from the drawings and the specifications what the tract configuration is before the project begins and what the tract configuration will be when the grading is completed. All this, however, is simply on paper and there yet remains the far greater task of actually preparing this site to conform to the drawings and specifications prepared in the engineering study. Traditionally, a survey crew would take the engineering documentation to the site and mark the site with stakes which convey to the grading equipment operators the instructions for grading the tract. By marks on the stakes, which are readable to those skilled in operating grading equipment, the depth of a cut or a fill, and the angle of slopes, etc., are defined. Unless the grading is unusually simple, however, it is insufficient for actual grading to proceed simply to mark by survey stakes the individual northings and eastings and to indicate the depth of the cut to be made or the fill to be made in particular locations. This marking would probably be sufficient for a large, flat tract of land, but would not be sufficient for grading of hilly terrain, or where multiple elevations or slopes are involved.
The survey crew, in nearly all grading projects of significant complexity, must place a great many stakes between the predetermined reference points to guide the grading machine operator. Typically, these stakes would be placed fairly close together, perhaps as close as two or three feet or even closer, where different slope, elevations, or curves intersect, and at least every ten to fifteen feet if there is any significant curvature or variation from a flat horizontal plane. The placement of these stakes is a very time consuming and expensive operation.
Even when all of the intermediate stakes have been placed, there remains a great challenge in actually producing a grade in accordance with the definition provided by the stakes. Frequently, the stakes are moved during the grading operation, perhaps by accidental contact by the grading blade or other grading tools, by being run over by the grading machine or other equipment, or by movement of the earth adjacent to the stake resulting in instability or movement of the stake. While the practice is frowned upon by civil engineers, there remains, nevertheless, a very common practice of simply driving the stake back in the ground and estimating that it is in the right location and right elevation. This practice, by the grading crew, frequently results in errors in grading and the necessity to go back and re-grade the tract or a portion of the tract. This procedure also nearly always requires that there be an additional individual who walks along beside the grading machine, uncovering the grading stakes and assisting the operator to position the grading tool at the proper elevation with respect to the grading stake. Thus, in addition to the grading machine operator, an assistant i required essentially on a full-time basis.
It will be apparent from the procedure just described that the present procedures for grading a tract of land are expensive and often lead to erroneous grading which either requires correction or by regrading the tract, or present problems during or after construction.
Techniques for grading are well known and are described in many test and treatises. References made to the following simply as exemplary of the treatises which describe various grading and excavating equipment and methods:
EXCAVATING & GRADING HANDBOOK, Nick Capachi, Craftsman Book Co., 542 Stevens Ave., Solana Beach, Calif. 92075;
CONSTRUCTION PLANNING EQUIPMENT AND METHODS, Third Addition, R. L. Peurfoy, McGraw-Hill Book Co., New York, (1979), and
EXCAVATION HANDBOOK, Horis K. Church, McGraw-Hill Book Co., New York, (1981).
There have been many efforts to automate various facets of the earth grading operation. For example, a device for automatic control of earth-moving machines is described in U.S. Pat. No. 3,009,271, Kuehne, et al., Nov. 21, 1961. Kuehne, et al. describes a method in which an analysis of the grading problem is made and recorded on precision cams or some similar method of presenting detailed information, punch cards for example. Range and azimuth information and elevational information are generated by a complex opticalmechanical system for indicating the depth the earth moving machine should make at a particular point. The Kuehne, et al. system relies upon an optical signal generator at a fixed geographic point, means for modulating the optical signal to include information relative to the cut to be made, and means for producing range and azimuth indicating signals which define the relative position of the optical radiating signal device and the earth moving machine. The distance and azimuth between the optical radiating device and the earth moving machine is the critical and controlling factor. In effect the Kuehne, et al. device was an optical direction finding and locator device which transmitted control information by means of a modulated optical system.
Another optical-mechanical system in which it is sought to overcome the difficulties in placing a large number of datum stakes as described, is disclosed in U.S. Pat. No. 3,046,681, Kutzler, July 31, 1962. The Kutzler system relies upon a pair of interacting optical radiation and receiving devices. In the Kutzler system, as in the Kuehne, et al. system, the range and azimuth relationships between the optical devices and the earth moving machine are the critical and controlling factors. Kutzler describes his apparatus in terms of means for establishing a reference data including a tri-planar reflecting device and means for selectively limiting the reflection of light thereon to define the location of the earth moving device with respect to the radiating devices.
Bourgeous, U.S. Pat. 3,126,653, Mar. 31, 1964, discloses a step point grade control device which uses an idler wheel and a measuring wheel to measure distance traveled and interrelates, in incremental steps, the distance traveled with suitably coded control tapes. The grading machine is provided with means driven by the measuring wheel which causes the control tape to move in proportion to the movement of the grading machine so that for particular points along the control tape, the machine occupies a corresponding point in the section of the road bed being graded. The Bourgeous system uses a rearward set of wheels which ride on the finished grade and serve to establish a reference plane utilized by the control apparatus to determine the depth and angle of cut and also serve as a surface on which the measuring wheel rotates freely so as to measure accurately the travel of the grading machine. The Bourgeous system is designed to make the final grading and the machine is controlled strictly by the tape which is driven by the measuring wheel. Bourgeous does indicate that it is possible to make different surveys and different tapes to make a multiple series of cut to ultimately obtain a finished grade. This requires, as pointed out by Bourgeous, that a second survey be made after the first effort at grading is made. The Bourgeous system, then, is a discrete step function system which has comparatively little flexibility and leaves few options for control by an operator. The stepping function of the Bourgeous system is a significant limitation on its utility in most grading operations. That limitation is overcome in the present invention. One important facet which is necessary to consider in the design and utilization of earth moving machinery is that there is required a considerable element of judgment on the part of the operator, especially during the initial grading phases. If the cut is too deep, the earth moving machine may simply stall, or ride over the earth, or deviate from its intended course. Except for the very final grading operation, it is, accordingly, impossible simply to define a course and direct the earth grading machine along that course, since it will usually be physically impossible for the earth grading machine to follow the prescribed course. Thus, it is essential that the operator be in control of the earth grading machine, except during the final grading passes, at which time it is possible to provide absolute control of the grading too.
Quite some years after the pioneering work of Townes in developing the laser, and with the industrialization of the laser, Studebaker, U.S. Pat. No. 3,494,426, Feb. 10, 1970, adapted the capabilities of laser control to earth grading equipment. Studebaker was able to obtain extremely accurate elevation control of the earth moving blade of a road grader over a wide working area by sweeping a laser beam periodically over the working area at a known elevation, thus establishing a reference plane of laser energy, then detecting the beam by suitable photoelectric devices carried on the vehicle, which are not interfered with by ambient light conditions, and then utilizing a signal generated by the photoelectric device to control the elevation of the blade. Devices of this type gained wide acceptance and are used in grading operations where high accuracy in obtaining a level tract or a uniform grade in the same plane are required. Studebaker found it important to maintain the mast in the vertical orientation regardless of the orientation of the earth moving machine.
Teach and Ramsey, U.S. Pat. No. 3,813,171, May 28, 1974, adapted the laser reference plane principal to earth trenching equipment and the like and provided a horizontal laser reference plane and a vertical laser reference plane to assure that, for example, a trench would be perpendicular to the plane of the earth, or at any desired angle.
Teach, U.S. Pat. No. 3,953,145, Apr. 27, 1976, further adapted an apparatus the laser reference beam principal in adapting an apparatus for controlling the elevation of a grading tool in a predetermined relationship to a fixed horizontal plane which is set by a laser beam which is periodically swept across the working area. The apparatus comprised a tape dispensing device carried by the machine and arranged to intermittently advance the tape past the tape reader. The tape carried two sets of indicia, one set indicating whenever a change in the height of the grading tool is required at a particular point and a second set of indicia indicating the distance between the points. A ground engaging wheel measured the travel of the machine and connected the tape dispensing device to advance the tape to the next set of indicia whenever the machine had traveled far enough to arrive at the next of the predetermined points. The Teach, U.S. Pat. No. 3,953,145, patent apparatus is similar to that of Bourgeous, U.S. Pat. No. 3,126,653, except that Teach utilizes the laser reference plane whereas Bourgeous used the optical range and azimuth system. As with Bourgeous, and the other prior art heretofore discussed, Teach would seem to be adequately adapted to making the final grading cut, or to laying pavement, which seems to be the principal application to which the Teach '145 invention is directed. These step function based systems are inadequate, however,in making preliminary cuts and in allowing the operator to exercise judgment in controlling the earth moving machine, as well as in providing ultimate control. The inability to control blade elevation along a continuous curve and the inability to control cross slope is a serious drawback of these and other prior art systems.
Johnson, U.S. Pat. No. 4,162,708, July 31, 1979, combined the rotating laser beam reference plane concept with a computer carried by the vehicle, operating under predetermined computer program to accurately control the grade in a given area. The specific disclosure of the Johnson '708 patent deals with a particular laser detector concept and construction. Johnson discloses, in rather broad and general terms, a computer controlled grading machine in which a computer receives signals indicative of the distance between a blade and a laser reference plane, the slope of the blade, the directions of steering of grading machine, a speed and distance sensor incorporated in the speedometer and odometer, and compares the actual position of the steering system with a preferred position defined by the computer program. The system has utility in the construction of highways, etc., which follow mathematically predictable courses. Other than the utilization of mathematically defined curves, etc., Johnson contains no disclosure as to any particular system of operation or system for carrying out a particular operation. With respect to the computer control of the earth grading equipment, Johnson discloses mechanisms for controlling the particular elements of the machine, but does not disclose an overall system capable of performing any functions other than the configuring of mathematically defined curves. Johnson speaks mostly in generalities and has little specific information regarding any particular computer controlled operation.
The present invention overcomes the difficulties described before, reducing manpower costs, providing the flexibility to grade the continuous curves and cross slopes of any configuration, and yet maintaining the judgmental control of a grading machine by the operator.